Vehicular occupant restraint systems usually include a seat belt harness comprised of a lap belt and a shoulder belt which merge at a clasp structured to releasibly engage a manual buckle mechanism. The buckle is typically attached by a flexible strap to the vehicle underbody to function as an anchor when the occupant restraint system is placed into use.
The buckle is normally positioned at or near the seat cushion on the inboard side of the seat for easy accessibility when joining or disjoining the seat belt harness and buckle assembly. Because the buckle is anchored to the underbody, a problem arises when the seat is adjusted between forward and rearward and/or raised and lowered positions to orient the driver or passenger in a comfortable position.
If the occupant is particularly small in stature, the seat will be articulated forwardly and upwardly to the maximum extent of the seat adjustment mechanism. This relative movement of the seat causes the underbody anchored buckle of the occupant restraint system to become positioned below and behind the seat cushion. Thus, a small statured occupant often has to search and grope for the buckle when joining and disjoining the seat belt harness. Searching for the buckle behind or below the seat cushion is particularly aggravated when in an unfamiliar vehicle, when low lighting conditions or disagreeable weather conditions exist. Also, with the buckle positioned below and behind the seat cushion of a forwardly adjusted seat, the seat belt harness may wrap around the edge of the seat cushion causing an uncomfortable condition.
Alternatively, if the occupant is large in stature, the seat assembly will be articulated completely rearwardly and in a lowered condition such that the buckle anchored to the underbody will become positioned significantly above and forwardly of the seat cushion. Thus, when the buckle is connected to the seat belt harness, the buckle may lay uncomfortably across the large occupant's leg or in some other way cause discomfort due to its position above the seat cushion.
The prior art has sought to overcome this problem by anchoring the buckle to a stationary fixed rail of the seat adjustment mechanism and attaching an upper portion of the buckle to the moveable seat frame. A hydraulic cylinder is provided between the seat frame and the fixed rail to account for relative movement between the fixed rail and seat frame.
For example, U.S. Pat. Nos. 4,993,747 and 4,037,132, both issued to Borlinghaus et al, on Feb. 19, 1991 and Aug. 6, 1991, respectively, and both assigned to the assignee of the subject invention, disclose buckle mechanisms including hydraulic cylinders. These vehicular seat assemblies include a fixed rail for attachment to a vehicle underbody or floor, a sliding rail movably carried on the fixed rail, a seat frame operatively supported above the sliding rail for receiving and supporting a vehicle seat cushion, an articulator means or some form of power seat adjustment mechanism interconnecting the seat frame and the sliding rail for moving the seat frame upwardly and angularly relative to the sliding rail, and a buckle means for releasibly clasping a seat belt harness relative to the fixed rail.
Although quite effective, the primary disadvantage of the assemblies disclosed in these Borlinghaus et al patents is that the hydraulic cylinder is exceptionally long and must be structured with an over-travel mechanism because of the large movement variability between the seat frame and the fixed rail. The Borlinghaus et al '747 reference teaches electrifying the hydraulic fluid to achieve a desired viscosity within the hydraulic cylinder. Over-travel mechanisms are required because the typical horizontal travel between the sliding rail and the fixed rail is approximately 8 inches, and the typical vertical travel provided by the articulator means is approximately 2 inches. Therefore, because the hydraulic cylinder is attached to the rearwardmost end of the fixed rail, the hydraulic cylinder must extend/contract a minimum of 8 inches travel in the horizontal direction and approximately 2 inches in the vertical direction, which results in a minimum diagonal vector travel of almost 9 inches.
Thus, the hydraulic cylinders disclosed in the Borlinghaus et al patents are expensive to manufacture because of their large size to accommodate travel limits and their relatively complex over-travel mechanisms provided. Further, the hydraulic cylinders in the Borlinghaus et al references are adapted primarily for two door model vehicles where the rear seat is not frequently used. The long hydraulic cylinders employed in such vehicles tend to crowd the feet of the rear seat occupants when the forward seat is moved to a forwardmost location and are susceptible to abrasion or damage from the feet of rear seat occupants and/or cargo. Hence, new constructions are needed to accommodate seat articulation and for enhancing the comfort of rear seated occupants.